Battery management system and battery management method

ABSTRACT

Provided are a battery management system and a battery management method using the same. According to the present invention, it is possible to select high-risk battery cells that are highly likely to be out of an operating voltage range by applying a change amount according to SoH for each of the battery cells to each SoC for each of the battery cells, and calculate the representative SoH of the battery pack based on the selected high-risk battery cells, and then calculate the actual usable capacity of the battery pack.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No.10-2020-0030806 filed Mar. 12, 2020, the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The following disclosure relates to a battery management system capableof selecting high-risk battery cells that are likely to be out of anoperating voltage range among a plurality of battery cells constitutinga battery pack, and calculating an actual usable capacity of the batterypack based on the selected battery cells, and a battery managementmethod using the same.

Description of Related Art

As a general method for estimating a battery state (state of charge(SoC), state of health (SoH), internal resistance, etc.) used in abattery management system (BMS) of an electric vehicle, there is amethod of determining a battery state by selecting a representativevoltage of a battery pack that represents a plurality of battery cells.

The battery management system calculates a current limit value at whichthe battery can be charged and discharged between an upper limit voltageduring charging and a lower limit voltage during discharging using thedetermined battery state. This is because if the voltage of the batterycell is repeatedly out of a boundary between the upper and lower limitvoltages, that is, the operating voltage range during the charging anddischarging, the battery cell deteriorates, and thus the battery life isadversely affected. However, in the actual battery pack, there is adeviation in the state of the respective battery cells from thebeginning of production. The deviation may further increase as theelectric vehicle is driven. When the deviation between the battery cellsincreases in this way, an error also increases in the estimation of thebattery state using the representative voltage of the plurality ofbattery cells.

FIG. 1A illustrates a change in a terminal voltage over time in the caseof an ideal battery pack. Referring to FIG. 1A, since each battery cellincluded in the ideal battery pack has the same internal resistance,current capacity, etc., and thus has a constant rate of decrease in theterminal voltage over time to have the same terminal voltage, there isno problem in determining the battery state using any one battery cellor an average voltage of the battery cells as a representative voltage.

In contrast, FIG. 1B illustrates a change in the terminal voltage overtime in the case of the actual battery pack. Referring to FIG. 1B, sinceeach battery cell included in the actual battery pack has differentinternal resistance, current capacity, etc., and thus has a differentrate of decrease in the terminal voltage over time, an error occurs whensimply estimating the battery state using any one battery cell or theaverage voltage of the battery cells as the representative voltage.

If an error occurs when estimating the battery state, an error occurseven when calculating a current limit value based on the stateestimation. In this case, battery cells that are out of the operatingvoltage range and continuously deteriorate may occur during the chargingand discharging, and thus the overall efficiency of the battery pack maybe reduced and the stability of the battery pack may be reduced, therebycausing the risk that the electric vehicle stops while driving.

Therefore, in order to prevent this, there is a need to grasp the stateof each of the plurality of battery cells constituting the battery pack,and select and specially manage high-risk battery cells that are likelyto deteriorate by first reaching the upper or lower limit of theoperating voltage among the battery cells.

RELATED ART DOCUMENT Patent Document

-   Korean Patent Laid-Open Publication No. 10-2013-0110355

SUMMARY OF THE INVENTION

An embodiment of the present invention is directed to providing a systemand method of selecting a high-risk battery cell which is likely todeteriorate by first reaching an upper or lower limit value of anoperating voltage among a plurality of battery cells.

Another embodiment of the present invention is directed to providing ansystem and method capable of calculating an actual usable capacity of abattery pack.

In one general aspect, a battery management system for selecting, from aplurality of battery cells constituting a battery pack, a high-riskbattery cell that has a risk that a terminal voltage during charging ora terminal voltage during discharging is out of an operating voltage,includes: a state information calculator that calculates stateinformation of each of the plurality of battery cells; and a cellselector that selects the high-risk battery cell using the stateinformation, in which the state information calculated by the stateinformation calculator includes at least one of a state of charge (SoC)and a state of health (SoH), and the cell selector selects the high-riskbattery cell by using the state information of at least one of the SoCof each of the battery cells and the SoH of each of the battery cells ata current measurement time point.

The cell selector may select the high-risk battery cell by applying achange amount of the SoC according to the SoH of each of the batterycells to the SoC of each of the battery cells at the current measurementtime point.

The cell selector may select a battery cell to be fully charged first asthe high-risk battery cell when applying the change amount of the SoCaccording to the SoH of each of the battery cells based on the SoC ofeach of the battery cells at the current measurement time point, andselects a battery cell to be fully discharged first as the high-riskbattery cell when applying the change amount of the SoC according to theSoH of each of the battery cells based on the SoC of each of the batterycells at the current measurement time point.

The cell selector may select a battery cell having the lowest SoH amongthe battery cells as the high-risk battery cell.

When a current flows into the selected high-risk battery cell at 1C-rate based on the initial usable capacity of the battery cells, thecell selector may calculate a representative SoH of the battery pack byapplying the following Equation 1 to K which is a summed value of a timefrom the current measurement time point until the battery cell to befully discharged first is fully discharged and a time from the currentmeasurement time point until the battery cell to be fully charged firstis fully charged.SoH _(pack) =K×100  [Equation 1]

(Here, SoH_(pack) is the representative SoH of the battery pack, and theunit of K is time (hr))

The battery management system may further include: a capacity calculatorthat calculates the actual usable capacity of the battery pack, in whichthe actual usable capacity of the battery pack calculated by thecapacity calculator may be calculated through the following Equation 2.CP _(pack) =SoH _(pack) ×CP _(BOL)  [Equation 2]

(Here, CP_(pack) is the actual usable capacity of the battery pack,SoH_(pack) is the representative SoH of the battery pack, and CP_(BOL)is the initial usable capacity of the battery cell)

In another general aspect, a battery management method using a batterymanagement system for selecting, from a plurality of battery cellsconstituting a battery pack, a high-risk battery cell that has a riskthat a terminal voltage during charging or a terminal voltage duringdischarging is out of an operating voltage, includes: calculating stateinformation of each of the plurality of battery cells; and selecting thehigh-risk battery cell using the state information, wherein the stateinformation includes at least one of SoC and SoH, and in the selectingof the high-risk battery cell, the high-risk battery cell is selected byusing the state information of at least one of the SoC of each of thebattery cells and the SoH of each of the battery cells at a currentmeasurement time point.

In the selecting of the high-risk battery cell, the high-risk batterycell may be selected by applying a change amount of the SoC according tothe SoH of each of the battery cells to the SoC of each of the batterycells at the current measurement time point.

In the selecting of the high-risk battery cell, a battery cell to befully charged first may be selected as the high-risk battery cell whenapplying the change amount of the SoC according to the SoH of each ofthe battery cells based on the SoC of each of the battery cells at thecurrent measurement time point, and a battery cell to be fullydischarged first may be selected as the high-risk battery cell whenapplying the change amount of the SoC according to the SoH of each ofthe battery cells based on the SoC of each of the battery cells at thecurrent measurement time point.

In the selecting of the high-risk battery cell, a battery cell having alowest SoH among the battery cells may be selected as the high-riskbattery cell.

The battery management method may further include: after the selectingof the high-risk battery cell, calculating a representative SoH of thebattery pack by applying the following Equation 3 to K which is a summedvalue of a time from the current measurement time point until thebattery cell to be fully discharged first is fully discharged and a timefrom the current measurement time point until the battery cell to befully charged first is fully charged, when a current flows into theselected high-risk battery cell at 1 C-rate based on the initial usablecapacity of the battery cells.SoH _(pack) =K×100  [Equation 3]

(Here, SoH_(pack) is the representative SoH of the battery pack, and theunit of K is time (hr))

The battery management method may further include: after the calculatingof the representative SoH of the battery pack, calculating the actualusable capacity of the battery pack through the following Equation 4.CP _(pack) =SoH _(pack) ×CP _(BOL)  [Equation 4]

(Here, CP_(pack) is the actual usable capacity of the battery pack,SoH_(pack) is the representative SoH of the battery pack, and CP_(BOL)is the initial usable capacity of the battery cell)

According to the present invention, the high-risk battery cell that ishighly likely to be out of the operating voltage range can be selectedby applying the change amount according to the SoH for each of thebattery cells to the SoC for each of the battery cells.

In addition, according to the present invention, the representative SoHof the battery pack based on the selected high-risk battery cells iscalculated, and then the actual usable capacity of the battery pack canbe calculated based on the calculated representative SoH.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram illustrating a change in a terminal voltage of abattery cell, which is included in an ideal battery pack, over time.

FIG. 1B is a diagram illustrating a change in a terminal voltage of abattery cell, which is included in an actual battery pack, over time.

FIG. 2 is a diagram illustrating the conventional battery managementsystem (BMS).

FIG. 3 is a diagram schematically illustrating a battery managementsystem according to the present invention.

FIG. 4 is a diagram illustrating a change amount of SoC according to SoHof each of the battery cells.

FIG. 5 is a diagram illustrating a method of calculating an actualusable capacity of a battery pack using a high-risk battery cell.

FIG. 6 is a flowchart illustrating a flow of a battery management methodaccording to the present invention.

DETAILED DESCRIPTION OF MAIN ELEMENTS

-   1: Conventional battery management system-   10: Conventional state information calculator-   12: Convention current calculator-   1000: Battery management system-   100: State information calculator-   200: Cell selector-   300: Capacity calculator-   400: Current calculator

DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail withreference to the accompanying drawings. In addition, a detaileddescription for the well-known functions and configurations that mayunnecessarily make the gist of the present invention unclear will beomitted.

A term “unit”, “module”, or the like, described in the specificationmeans a unit of processing at least one function or operation and may beimplemented by hardware or software or a combination of hardware andsoftware.

FIG. 2 is a diagram illustrating the conventional battery managementsystem.

Referring to FIG. 2 , the conventional battery management system 10receives a pack representative voltage, current, and temperature fromthe battery pack 20, and calculates a representative state of charge(SoC) of the battery pack 20, a representative state of health (SoH) ofthe battery pack 20, and a representative internal resistance Rs of thebattery pack 20 in the state information calculator 11. By using therepresentative SoC, the representative SoH, and the representativeinternal resistance Rs calculated in this way, the current calculator 12calculates a current limit value that allows the battery pack 20 to becharged and discharged within the operating voltage range, and thecurrent limit value is transferred to a vehicle control unit (VCU) 30that may adjust a load to make a current within the current limit valueflow into the battery pack 20.

In this case, the load may be an inverter for controlling a motor, acharging device for charging the battery pack 20, or the like.

However, as described above, unlike an ideal battery pack, in the caseof an actual battery pack, the internal resistance, the currentcapacity, and the like of each battery cell included in the battery packare different from each other, and as a result, reduction rates in aterminal voltage over time are different from each other, and adeviation in the terminal voltage becomes severe over time.

Therefore, for the stability and efficiency of the battery pack, thereis a need to select and specially manage high-risk battery cells amongbattery cells, which are likely to deteriorate by first reaching upperor lower limits of the operating voltage.

In addition, there is a need to select the high-risk battery cells inorder to accurately calculate the limit value of the current allowed inthe battery pack.

FIG. 3 is a diagram schematically illustrating a battery managementsystem according to the present invention.

Referring to FIG. 3 , a battery management system 1000 according to thepresent invention includes a state information calculator 100 and a cellselector 200.

Here, the state information calculator 100 may receive at least one ofthe temperature of the battery pack 20 or each of the battery cellsmeasured from the battery pack 20, the voltage of each of the batterycells, and the current of the battery pack 20 to calculate at least oneof the state of charge (SoC) and the state of health (SoH) of each ofthe battery cells as the state information. The state information ofeach of the battery cells thus calculated is transmitted to the cellselector 200 in order to select the high-risk battery cell.

At this time, the voltage, current, temperature, and the like aremeasured at predetermined time intervals.

Meanwhile, since a method for calculating SoC or SoH using the voltage,current, and temperature is a known technique, a detailed descriptionthereof will be omitted in the present invention.

The cell selector 200 is a component that selects the high-risk batterycells using the state information of each of the battery cells receivedfrom the state information calculator 100.

More specifically, the cell selector 200 may select the high-riskbattery cell using the state information of at least one of the SoC ofeach of the battery cells and the SoH of each of the battery cells atthe current measurement time point.

FIG. 4 is a diagram illustrating a change amount of SoC according to SoHof each of the battery cells.

Referring to FIG. 4 , the cell selector 200 may receive the SoC of eachof the battery cells at a current measurement time point t_(k) from thestate information calculator 100, and apply a change amount of the SoCaccording to the SoH of each of the battery cells to the SoC of each ofthe battery cells, thereby selecting the high-risk battery cells.

For example, as a result of applying the change amount of the SoCaccording to the SoH of each of the battery cells to the SoC of each ofthe battery cells at the current measurement time point t_(k), the cellselector 200 may select a battery cell that first reaches 100% SoC, thatis, a battery cell to be fully charged first, as a high-risk batterycell.

Here, the meaning of applying the change amount of the SoC according tothe SoH described above means that the SoH value of each of the batterycells is converted into a slope and applied as the change amount of SoCof the corresponding battery cell.

In order to describe in more detail, the following Equations 1 to 3 willbe described.

The discharge capacity of the battery cell is shown in Equation 1 below.

$\begin{matrix}{{{Discharge}{capacity}{of}{cell}} = {\int_{0}^{t}{{I(t)}{dt}}}} & \left\lbrack {{Equation}1} \right\rbrack\end{matrix}$

At this time, since the battery cells are connected in series, the samecurrent is applied to all battery cells, and thus the discharge capacityof each of the battery cells is the same.

Meanwhile, SoC may be represented by Equation 2 below.

$\begin{matrix}{{SoC} = {\frac{{Remaining}{capacity}{of}{cell}}{{Total}{capacity}{of}{cell}} = {\frac{\begin{matrix}{{{Initial}{capacity}{of}{cell} \times {SoH}} -} \\{{Discharge}{capacity}{of}{cell}}\end{matrix}}{{Initial}{capacity}{of}{cell} \times {SoH}} = {1 - \frac{{Discharge}{capacity}{of}{cell}}{{Initial}{capacity}{of}{cell} \times {SoH}}}}}} & \left\lbrack {{Equation}2} \right\rbrack\end{matrix}$

Therefore, when a current I has a constant value, the function of theSoC over time satisfies Equation 3 below in relation to the SoH.

$\begin{matrix}{{{SoC}(t)} = {1 - {\frac{I}{{Initial}{capacity}{of}{cell} \times {SoH}}t}}} & \left\lbrack {{Equation}3} \right\rbrack\end{matrix}$

As a result, as a battery cell with a small SoH, a straight line graphrepresenting the SoC over time has a steeper slope and reaches 100% SoCor 0% SoC first.

In the example of FIG. 4 , it can be seen that cell A is a battery cellto be fully charged by reaching 100% SoC first. At this time, the cellselector 200 selects cell A as a high-risk battery cell.

On the contrary, when the representative SoC is selected based on abattery cell other than cell A among several battery cells having statedeviations from each other, or an average value of SoC is selected asthe representative SoC, if the cell A is charged first in the state inwhich other battery cells (cells B, C, and D) are not yet fully charged,the battery cells may be overcharged by exceeding the upper limit of theoperating voltage, which is repeated and thus the cell A deteriorates,thereby adversely affecting the life of the entire battery pack.

Alternatively, as a result of applying the change amount of the SoCaccording to the SoH of each of the battery cells to the SoC of each ofthe battery cells at the current measurement time point t_(k), the cellselector 200 may select a battery cell that first reaches 0% SoC, thatis, a battery cell to be fully discharged first, as a high-risk batterycell.

In the example of FIG. 4 , it can be seen that cell C is a battery cellto be fully charged by reaching 0% SoC first. At this time, the cellselector 200 selects cell C as a high-risk battery cell.

On the contrary, when the representative SoC is selected based on abattery cell other than cell C among several battery cells having statedeviations from each other, or an average value of SoC is selected asthe representative SoC, if the cell C is discharged first in the statein which other battery cells (cells A, B, and D) are not yet fullydischarged, the battery cells may be overdischarged to the lower limitof the operating voltage, which is repeated and thus the cell Cdeteriorates, thereby adversely affecting the life of the entire batterypack.

Alternatively, the cell selector 200 may select a battery cell havingthe lowest SoH among the battery cells as a high-risk battery cell.

The reason of selecting the battery cells with low SoH as the high-riskbattery cell is that the battery cells with low SoH may have undergonedeterioration due to driving or have high internal resistance due totolerances or defects at the time of manufacture, and the terminalvoltage of the battery cell is highly likely to be out of the operatingvoltage when the battery cell is charged or discharged with the samecurrent.

In the example of FIG. 4 , since the cell C having the largest slope isa battery cell having the lowest SoH, the cell C is selected as ahigh-risk battery cell.

Meanwhile, the above-described operating voltage is a voltage range inwhich the battery cell may be stably charged and discharged withoutdeteriorating. For example, the upper limit of the operating voltage maybe predetermined as 4.2V (SoC 100%) and the lower limit may bepredetermined as 2.7V (SoC 0%).

As described above, the cell selector 200 may select the high-riskbattery cells and then provide information on the selected high-riskbattery cells to the current calculator 400.

Meanwhile, the current calculator 400 may divide the change amount inthe terminal voltage when it is assumed that the terminal voltage of theselected high-risk battery cell reaches the upper or lower limit of theoperating voltage at the next measurement time point by the internalresistance of the high-risk battery cell to calculate the current limitvalue.

In addition, when there are two or more calculated high-risk batterycells, the current calculator 400 may calculate, as a final currentlimit value, the smallest of the current limit values calculated basedon each high-risk battery cell.

At this time, since the current limit value is calculated usinginformation on the high-risk battery cells among all battery cells, itis calculated as a more accurate value than when calculated through theselection of a representative value as in the related art. In addition,since the current limit value is calculated using only the informationon the high-risk battery cell, not the information on all the batterycells, the calculation load does not increase significantly compared tothe prior art.

Meanwhile, the battery management system 1000 of the present inventionmay further include a capacity calculator 300 that calculates an actualusable capacity of the battery pack.

FIG. 5 is a diagram for explaining how the capacity calculator 300calculates an actual usable capacity of a battery pack using a high-riskbattery cell, which will be described below with further reference toFIG. 5 .

Before calculating the actual usable capacity of the battery pack, thecell selector 200 may calculate a value K summed by calculating a timefrom the current measurement time point t_(k) until the battery cell tobe fully discharged first is fully discharged and a time from thecurrent measurement time point t_(k) until the battery cell to be fullycharged first is fully charged when it is assumed that a current flowsinto through the selected high-risk battery cells at 1 C-rate based onthe initial usable capacity of the battery cells.

Here, the time until the battery cell to be fully discharged first isfully discharged and the time until the battery cell to be fully chargedfirst is fully charged are calculated using the SoC at the currentmeasurement time point t_(k) of the corresponding battery cells,respectively.

At this time, the C-rate is a discharge rate that means a current rate,and may be expressed as a charge/discharge current A of a batterycell/capacity Ah of a battery cell.

In other words, it means that when a battery cell with an initial usablecapacity of 200 Ah is discharged at 1 C-rate, the battery cell may beused for 1 hour, and when the battery cell with an initial usablecapacity of 200 Ah is discharged at 2 C-rate, the battery cell may beused for 0.5 hours.

For example, referring to FIG. 5 , the cell C, which is the battery cellto be fully discharged first, has 50% SoC at the current measurementtime point t_(k), so the cell selector 200 may calculate, as 0.5*60(hr)=0.5 hr, the time until the cell C is fully discharged when acurrent flows at 1 C-rate.

In addition, since the cell A, which is the battery cell to be fullycharged first, has 70% SoC at the current measurement time point, thecell selector 200 may calculate, as 0.3*60 (hr)=0.3 hr, the time untilthe cell A is fully charged when a current flows at 1 C-rate.

The cell selector 200 may calculate K by summing the time thuscalculated, and then calculate the representative SoH of the batterypack by applying Equation 4 below.SoH _(pack) =K×100  [Equation 4]

At this time, SoH_(pack) is a representative SoH of the battery pack,and the unit of K is time (hr).

Here, since K is a value calculated using the battery cell to be fullycharged first and the battery cell to be fully discharged first amongthe battery cells, the representative SoH of a highly reliable batterypack may be obtained by using the K.

In the example of FIG. 5 , K is calculated as 0.5+0.3=0.8, and therepresentative SoH of the battery pack is calculated as 80% throughEquation 4 above.

By using the representative SoH of the battery pack thus calculated, thecapacity calculator 300 may calculate the actual usable capacity of thebattery pack through Equation 5 below.CP _(pack) =SoH _(pack) ×CP _(BOL)  [Equation 5]

Here, CP_(pack) is the actual usable capacity of the battery pack,SoH_(pack) is the representative SoH of the battery pack calculated bythe cell selector 200, and CP_(BOL) is the initial usable capacity ofthe battery cell.

In the example of FIG. 5 , since the representative SoH of the batterypack is calculated as 80%, when the initial usable capacity (CP_(BOL))of the battery cell is 200 Ah, the actual usable capacity of the batterypack is calculated as 160 Ah.

As described above, the battery management system of the presentinvention may select the high-risk battery cells that are highly likelyto be out of the operating voltage range by applying the change amountaccording to the SoH for each of the battery cells to each SoC for eachof the battery cells. Since the high-risk battery cells thus selectedmay be used as a reference battery cell for calculating the optimizedbattery pack current limit value, the current limit value may beaccurately calculated and the stability of the battery pack may beimproved.

In addition, according to the present invention, the battery managementsystem may calculate the actual available capacity of the battery packafter calculating the representative SoH of the battery pack based onthe selected high-risk battery cells.

In addition, in the battery management system according to the presentinvention, since the selected high-risk battery cells are battery cellsthat are likely to quickly deteriorate among the plurality of batterycells constituting the battery pack, the high-risk battery cells amongall the battery cells included in the battery pack may be continuouslymanaged as targets to be determined whether to be replaced first. Thatis, since the entire battery pack does not need to be replaced, theefficient maintenance and management of the battery pack is possible.

FIG. 6 is a flow chart illustrating a flow of a battery managementmethod according to the present invention, and the battery managementmethod according to the embodiment of the present invention may beperformed by the battery management system 1000 described above.

Referring to FIG. 6 , in the battery management method according to anexemplary embodiment of the present invention, first, the stateinformation calculator 100 calculates state information of each of aplurality of battery cells (S100).

More specifically, in step (S100), the state information calculator 100may receive at least one of the temperature of the battery pack 20 oreach of the battery cells measured from the battery pack 20, the voltageof each of the battery cells, and the current of the battery pack 20 tocalculate at least one of the state of charge (SoC) and the state ofhealth (SoH) of each of the battery cells as the state information. Thestate information of each of the battery cells thus calculated istransmitted to the cell selector 200 in order to select the high-riskbattery cell.

Next, the cell selector 200 selects a high-risk battery cell using thestate information (S200).

At this time, in the step (S200), the cell selector 200 may select thehigh-risk battery cell using the state information of at least one ofthe SoC of each of the battery cells and the SoH of each of the batterycells at the current measurement time point.

More specifically, in the step (S200), the cell selector 200 may selectthe high-risk battery cell by applying the change amount of SoCaccording to the SoH of each of the battery cells to SoC of each of thebattery cells at the current measurement time point.

Here, the cell selector 200 may select a battery cell to be fullycharged first as the high-risk battery cell when applying the changeamount of the SoC according to the SoH of each of the battery cellsbased on the SoC of each of the battery cells at the current measurementtime point, and select a battery cell to be fully discharged first asthe high-risk battery cell when applying the change amount of the SoCaccording to the SoH of each of the battery cells based on the SoC ofeach of the battery cells at the current measurement time point.

Meanwhile, the battery management method according to the presentinvention may further include a step (S300) of calculating arepresentative SoH of the battery pack by applying the above Equation 4to K which is a summed value of a time from the current measurement timepoint until the battery cell to be fully discharged first is fullydischarged and a time from the current measurement time point until thebattery cell to be fully charged first is fully charged, if a currentflows into the selected high-risk battery cell at 1 C-rate based on theinitial usable capacity of the battery cells, after selecting thehigh-risk battery cell (S200).

At this time, the step (S300) may be performed in the cell selector 200of the battery management system 1000.

In addition, the cell selector 200 may calculate the time until thebattery cell to be fully discharged first is fully discharged and thetime until the battery cell to be fully charged first is fully chargedusing the SoC at the current measurement time point of the correspondingbattery cells, respectively.

Meanwhile, the battery management method of the present invention mayfurther include calculating the actual usable capacity of the batterypack through Equation 5 (S400) after calculating the representative SoHof the battery pack (S300).

At this time, the step (S400) may be performed in the capacitycalculator 300 of the battery management system 1000.

In addition, a more detailed description of the battery managementmethod of the present invention may be replaced by the above descriptionof the battery management system 1000 according to the presentinvention.

As described above, the battery management method of the presentinvention may select the high-risk battery cells that are highly likelyto be out of the operating voltage range by applying the change amountaccording to the SoH for each battery cell to each SoC for each batterycell. Since the high-risk battery cells thus selected may be used as areference battery cell for calculating the optimized battery packcurrent limit value, the current limit value may be accuratelycalculated and the stability of the battery pack may be improved.

In addition, the battery management method according to the presentinvention may calculate the actual available capacity of the batterypack after calculating the representative SoH of the battery pack basedon the selected high-risk battery cells.

In addition, in the battery management method according to the presentinvention, since the selected high-risk battery cells are battery cellsthat are likely to quickly deteriorate among the plurality of batterycells constituting the battery pack, the high-risk battery cells amongall the battery cells included in the battery pack may be continuouslymanaged as targets to be determined whether to be replaced first. Thatis, since the entire battery pack does not need to be replaced, theefficient maintenance and management of the battery pack is possible.

Although the present disclosure has been described with reference to theexemplary embodiments and the accompanying drawings, the presentdisclosure is not limited to the above-mentioned exemplary embodiments,but may be variously modified and changed from the above description bythose skilled in the art to which the present disclosure pertains.Therefore, the scope and spirit of the present invention should beunderstood only by the following claims, and all of the equivalences andequivalent modifications to the claims are intended to fall within thescope and spirit of the present invention.

What is claimed is:
 1. A battery management system for selecting, from aplurality of battery cells constituting a battery pack, a high-riskbattery cell that has a risk that a terminal voltage during charging ora terminal voltage during discharging is out of an operating voltage,the battery management system comprising: a state information calculatorthat calculates state information of each of the plurality of batterycells; and a cell selector that selects the high-risk battery cell usingthe state information, wherein the state information calculated by thestate information calculator includes at least one of a state of charge(SoC) and a state of health (SoH), wherein the cell selector selects thehigh-risk battery cell by using the state information of at least one ofthe SoC of each of the plurality of battery cells and the SoH of each ofthe plurality of battery cells; and wherein the cell selector selectsthe high-risk battery cell by applying a change amount of the SoCaccording to the SoH of each of the plurality of battery cells to theSoC of each of the plurality of battery cells at a current measurementtime point.
 2. The battery management system of claim 1, wherein thecell selector selects a battery cell to be fully charged first as thehigh-risk battery cell when applying the change amount of the SoCaccording to the SoH of each of the plurality of battery cells based onthe SoC of each of the plurality of battery cells at the currentmeasurement time point, and selects a battery cell to be fullydischarged first as the high-risk battery cell when applying the changeamount of the SoC according to the SoH of each of the plurality ofbattery cells based on the SoC of each of the plurality of battery cellsat the current measurement time point.
 3. The battery management systemof claim 2, wherein when a current flows into the selected high-riskbattery cell at 1 C-rate based on the initial usable capacity of theplurality of battery cells, the cell selector calculates arepresentative SoH of the battery pack by applying the followingEquation 1 to K which is a summed value of a time from the currentmeasurement time point until the battery cell to be fully dischargedfirst is fully discharged and a time from the current measurement timepoint until the battery cell to be fully charged first is fully charged,SoH _(pack) =K×100   [Equation 1] where SoH_(pack) is the representativeSoH of the battery pack, and the unit of K is time (hr).
 4. The batterymanagement system of claim 3, further comprising: a capacity calculatorthat calculates the actual usable capacity of the battery pack, whereinthe actual usable capacity of the battery pack calculated by thecapacity calculator is calculated through the following Equation 2,CP _(pack) =SoH _(pack) ×CP _(BOL)   [Equation 2] where CP_(pack) is theactual usable capacity of the battery pack, SoH_(pack) is therepresentative SoH of the battery pack, and CP_(BOL) is the initialusable capacity of the battery cell.
 5. The battery management system ofclaim 1, wherein the cell selector selects a battery cell having thelowest SoH among the plurality of battery cells as the high-risk batterycell.
 6. A battery management method using a battery management systemfor selecting, from a plurality of battery cells constituting a batterypack, a high-risk battery cell that has a risk that a terminal voltageduring charging or a terminal voltage during discharging is out of anoperating voltage, the battery management method comprising: calculatingstate information of each of the plurality of battery cells; andselecting the high-risk battery cell using the state information,wherein the state information includes at least one of SoC and SoH, andthe high-risk battery cell is selected by using the state information ofat least one of the SoC of each of the plurality of battery cells andthe SoH of each of the plurality of battery cells in the selecting ofthe high-risk battery cell, and wherein the high-risk battery cell isselected by applying a change amount of the SoC according to the SoH ofeach of the plurality of battery cells to the SoC of each of theplurality of battery cells at a current measurement time point.
 7. Thebattery management method of claim 6, wherein in the selecting of thehigh-risk battery cell, a battery cell to be fully charged first isselected as the high-risk battery cell when applying the change amountof the SoC according to the SoH of each of the plurality of batterycells based on the SoC of each of the plurality of battery cells at thecurrent measurement time point, and a battery cell to be fullydischarged first is selected as the high-risk battery cell when applyingthe change amount of the SoC according to the SoH of each of theplurality of battery cells based on the SoC of each of the plurality ofbattery cells at the current measurement time point.
 8. The batterymanagement method of claim 6, wherein in the selecting of the high-riskbattery cell, a battery cell having a lowest SoH among the plurality ofbattery cells is selected as the high-risk battery cell.
 9. The batterymanagement method of claim 6, further comprising: after the selecting ofthe high-risk battery cell, calculating a representative SoH of thebattery pack by applying the following Equation 3 to K which is a summedvalue of a time from the current measurement time point until thebattery cell to be fully discharged first is fully discharged and a timefrom the current measurement time point until the battery cell to befully charged first is fully charged, when a current flows into theselected high-risk battery cell at 1 C-rate based on the initial usablecapacity of the plurality of battery cells,SoH _(pack) =K×100   [Equation 3] where SoH_(pack) is the representativeSoH of the battery pack, and the unit of K is time (hr).
 10. The batterymanagement method of claim 9, further comprising: after the calculatingof the representative SoH of the battery pack, calculating the actualusable capacity of the battery pack through the following Equation 4,CP _(pack) =SoH _(pack) ×CP _(BOL)   [Equation 4] wherein CP_(pack) isthe actual usable capacity of the battery pack, SoH_(pack) is therepresentative SoH of the battery pack, and CP_(BOL) is the initialusable capacity of the battery cell.